• There are 3.1 billion letters in the DNA code of each of the 100 trillion cells in the human body

• Four nitrogenous bases of the DNA alphabet, represented by the letters A, C, G and T and arranged in pairs, carry the instructions for making all organisms. Each block of three letters corresponds to a single amino acid

• There are 20 different amino acids used in an array of combinations to produce proteins as different as keratin in hair and haemoglobin in blood

• At 30,000 to 40,000, humans have far fewer genes than expected. The nematode worm has 18,000

• Between humans, DNA differs by only 0.2 per cent